Vehicular lock systems with so-called antitheft protection are described in commonly owned Pat. Nos. 4,440,006, 4,342,209, and 4,364,249. They each have a door latch settable in an unlocked position in which the controlled door, hood, or trunk can be opened without a key, a locked position permitting manual opening of the controlled door, hood, or trunk only by a key, and an antitheft position preventing such manual opening even with the key. At least one of the door latches in each of these systems, normally termed the master latch, can be directly set in the antitheft position to indirectly set the other latches of the vehicle in their antitheft positions. Thus with such an arrangement the antitheft setting makes the vehicle very secure, as only the master latch that can set this position can move the slave latches back into locked positions from which they can be moved to the unlocked positions like standard latches.
Such a vehicular lock system is used in combination with a battery and at least each slave latch has an electric servomotor powerable by the battery for displacement of the latch between at least the antitheft and locked positions. The control unit is connected between the battery and the controller for feeding the battery power to the servomotor for setting the latch at least in the antitheft and locked positions, depending on how the control unit is being operated or energized. As a rule, therefore the systems are of the central locking type that can also all be locked or unlocked from the master latch.
The control unit is typically operated by one of the latches or by a separate switch which can only be operated by a special key, for instance of the type described in U.S. Pat. Nos. 4,320,639 and 4,357,815, so that only the person possessing the master key can set the system in the antitheft position or take it out of the antitheft setting. This allows, for instance, a car owner to always keep this master key, while giving out to car-park operators and the like keys only effective to move the latches between the locked and unlocked positions so that even if these keys fall into the wrong hands the vehicle can be effectively locked up.
It is also possible to be able to move the system from the antitheft position to the locked position by means of a sophisticated electronic arrangement of the type described in copending patent application No. 568,610 and copending patent application No. 555,471 of W. Bongard et al. These coded arrangements allow remote operation of the control unit by means of a radio-frequency transmitter and are normally very secure.
Thus such arrangements require an on-board power source, usually the motor-vehicle battery although a separate source can be provided. If the voltage of the source drops below a predetermined minimum level, for instance when the lights or radio are accidentally left on or when the vehicle is stored long-term, the lock system can get stuck in the antitheft position since the power available is insufficient to operate the servomotors or power the receiver.
The result is therefore that the user is locked out of his or her vehicle. When the lock system is particularly secure, it might have to be forced to open up the vehicle, something that can result in costly damage.